The crevice corrosion resistance of alloys 625 (UNS No.N06625) and 22 (UNS No.N06022) was compared on the basis of critical potentials for stabilization, and repassivation as well as crevice stabilization rates. The effects of temperature, anion composition in 5 M LiCl based electrolytes, and oxide aging were examined. Repassivation potentials measured at 95°C were similar for both alloys and were not greatly influenced by bulk electrolyte composition, pH, or accumulated anodic charge. However, a decrease in temperature raised repassivation potentials for alloy 22 in comparison to 625. Crevice corrosion stabilization properties of alloys 625 (UNS No.N06625) and 22 (UNS No.N06022) were clearly influenced by temperature and electrolyte composition but not bulk solution pH. Crevice stabilization occurred at more active potentials in 5 M LiCl electrolytes with a molar ratio of chloride to total oxyanions of 100:1 (e.g. 0.05 M Na2SO4 + NaNO3) compared to 1:1 (e.g. 1 M LiCl, 1 M Na2SO4 + NaNO3). A greater potential driving force was required to maintain the same crevice generation rate (λ) for the 10:1 ratio electrolyte (0.5 M Na2SO4 + NaNO3) compared to the 100:1 ratio.

Subject
Transpassivation, Composition, Corrosion rate, Repassivation, Repassivation potentials, Dissolution, Probability, Crevices, Crevice corrosion, Alloys, Electrochemical potential, Electrolytes, Electrode potential
Keywords:
alloy 22 alloy 625, crevice corrosion, chloride, critical crevice potential, critical repassivation potential, cyclic potentiodynamic polarization
Government work published by the Association for Materials Protection and Performance (AMPP) with permission of the author(s). Positions and opinions advanced in this work are those of the author(s) and not necessarily those of AMPP. Responsibility for the content of the work lies solely with the author(s).
2001
GOV
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